Rotary electric machine

ABSTRACT

A rotary electric machine comprises a rotating shaft  7  rotatably supported by bearings  2, 3,  a rotor  23  attached integrally with the rotating shaft  7,  and a stator  5  arranged facing the rotor  23.  The stator  5  includes a plurality of coils arranged substantially in a circular (annular) form in a rotating direction of the rotating shaft  7.  The rotor  23  includes a circular-disc rotor yoke  26  made of a ferromagnetic material, such as iron. Depressed portions and raised portions  28  on a surface of the rotor yoke  26  facing the stator  5,  except for the center portion, are arranged in a circumferential direction of the rotor yoke  26.  N-pole magnets  29  and S-pole magnets  30  are alternately arranged in the depressed portions  27.  Therefore, in addition to torque generated by the magnets  29, 30,  reluctance torque is generated between the raised portions  28  on the rotor yoke side  26  and the teeth on the stator side  25,  thus making it possible to increase the range of rotation speeds of the motor.

TECHNICAL FIELD

[0001] The present invention relates to a rotary electric machineapplied to PM motors (permanent magnet type synchronous motors) used inelectric motorcars.

BACKGROUND ART

[0002] Among axial-gap type PM motors, one that is shown in FIG. 13 hasbeen well known.

[0003] As shown in FIG. 13, this motor is so structured as to bearranged in a housing (frame) 1, and comprises a rotating shaft 7rotatably supported by bearings 2, 3 fixed to the housing 1, a rotor 4integrally attached to the rotating shaft 7, and a stator 5 arrangedfacing the rotor 4 and fixed to the housing 1.

[0004] The rotor 4 is made of a circular disc 6 of a ferromagneticmaterial, such as iron, and the rotating shaft 7 is mounted at thecenter of the disc 6 and rotatably supported at both ends thereof by thebearings 2, 3. On the surface of the circular disc 6 which faces thestator 5, N-pole magnets 8 and S-pole magnets 9 are arranged alternatelyin the circumferential direction as shown in FIG. 14.

[0005] The stator 5 comprises an annular stator yoke 10 fixed to thehousing 1, and a plurality of teeth 11, which are press-fitted in aplurality of holes formed in the circumferential direction of the statoryoke 10. The stator teeth 11 are wound with coils 12 of wire.

[0006] Meanwhile, in electric cars, an in-wheel motor is mounted in thewheel to realize independent drive of the wheel. The in-wheel motor,which includes a reduction gear (change gearbox), is required to beflatter and thinner in structure. Flat-type PM motors such as the onementioned above will find application as an in-wheel motor with areduction gear.

[0007] In conventional axial-gap PM motors mentioned above, however,because they are incapable of utilizing reluctance torque, when they areused for in-wheel motors in electric-powered cars, there is a problemthat the available range of rotation speed N is narrow.

[0008] Incidentally, the above-mentioned axial-gap type PM motor may beused as a generator.

[0009] Therefore, when used in a motorcycle or the like, in addition tothe use as a starter motor to start the engine, and after the engine hasstarted, this motor may be switched to a generator mode by using thedriving force of the engine. This motor is hereafter referred to astarter-motor-cum-generator.

[0010] In other words, the starter-motor-cum-generator is used as astarter motor to start the engine and after the engine has started, itis used as a generator.

[0011] When the axial-gap type motor is used as astarter-motor-cum-generator as described above, the motor needs togenerate a high torque to start the engine. A general method to realizea high torque has been to increase the magnetic force of the magnet ofthe motor.

[0012] With a conventional axial-gap type motor, since there is littlehope that this motor gives reluctance torque, there has been no otherchoice but to increase the magnetic force of the magnet.

[0013] However, when the axial-gap motor is used as thestarter-cum-generator, after the engine has started, the motor switchesits operation to a generator mode, and need not generate a high torque.On the contrary, if the magnetic force of the motor magnet is increasedto generate a high torque, when the generator is driven at high speed togenerate electric power, the battery is likely to be overcharged, sothat it is necessary to provide a voltage reducing circuit to protectbatteries.

[0014] If the starter-motor-cum-generator is to be formed by using anaxial-gap motor, the magnetic force of the motor magnet is desired to belarge to secure a high torque at low rotation speed (when starting acar). However, to suppress overcharging of the battery at high rotationspeed, there arises a contradictory demand to reduce the magnetic forceof the motor magnet.

[0015] Therefore, an object of the present invention is to provide arotary electric machine which is capable of utilizing reluctance torquewhen this rotary electric machine is used as a motor and therebyincreasing the range of rotation speeds of the motor.

[0016] Another object of the present invention is to provide a rotaryelectric machine capable of preventing overcharge of the battery in itshigh-speed rotation and obviating the use of the voltage-reducingcircuit when the rotary electric machine is used astarter-motor-cum-generator in vehicles, such as motorcycles.

DISCLOSURE OF THE INVENTION

[0017] According to the present invention, there is provided a rotaryelectric machine comprising a stator having a plurality of coilsarranged in a substantially circular form around an axis and a rotorrotatable about the axis relative to the stator, wherein the rotorcomprises a rotor yoke facing the coils and having a gap in axialdirection, wherein the rotor yoke is made of a circular disc of aferromagnetic material, and wherein depressed and raised portions areprovided alternately in a circumferential direction on a surface of therotor yoke facing the coils, and N-pole magnets and S-pole magnets arealternately arranged in the depressed portions.

[0018] According to the present invention of a structure describedabove, the raised portions are formed between the N-pole magnets and theS-pole magnets on the rotor yoke side, and the raised portions face thecoils on the stator side. Therefore, supposing that the invention is amotor, a reluctance torque can be generated between the raised portionson the rotor yoke side and the teeth (coils) of the stator side, makingit possible to increase the range of rotation speed of the motor.

[0019] According to the present invention, since raised portions areprovided on the rotor yoke, the quantity of the magnet in use can bereduced by an amount due to that structural betterment than before,which makes it possible to decrease production cost.

[0020] Further according to the present invention, the magnetic force ofthe magnet can be made smaller than before, but a reluctance torque canbe generated as described above. Therefore, when this invention isapplied in forming a starter-motor-cum-generator for vehicles, such asmotorcycles, a high torque can be obtained by using the reluctancetorque at low rotation speed (as in starting a car), and because themagnetic force of the magnets is made small, the battery is preventedfrom being overcharged at high rotating speed, a fact which obviates theneed to use the voltage-reducing circuit.

[0021] Further according to the present invention, there is provided arotary electric machine comprising a stator having a plurality of coilsarranged in a substantially circular form around an axis and a rotorrotatable about the axis relative to the stator, wherein said rotorcomprises a rotor yoke facing the coils and having a gap in axialdirection, wherein the rotor yoke is made of a circular disc of aferromagnetic material, wherein a corrugated region having raised anddepressed cross-sections alternating with each other is formed in acircumferential direction of the rotor yoke and magnets are arranged inthe depressed portions, and wherein out of all depressed portions, inthose depressed portions on a surface side of the rotor yoke facing thecoils, N-pole magnets and S-pole magnets are arranged alternately.

[0022] According to the invention of the structure as described, on therotor yoke side, the raised portions are formed, each sandwiched betweenan N-pole magnet and an S-pole magnet, and the raised portions face thecoils on the stator side. For this reason, when the present invention isapplied in forming a motor, it is possible to generate a reluctancetorque at the raised portions on the yoke side in collaboration with theteeth on the stator side, and thereby increase the range of rotationspeed of the motor.

[0023] Further according to the present invention, the magnetic force ofthe magnet can be made smaller than before, but a reluctance torque canbe generated as described above. Therefore, when this invention isapplied in forming a starter-motor-cum-generator for vehicles, such asmotorcycles, a high torque can be obtained by using the reluctancetorque at low rotation speed (as in starting a car), and because themagnetic force of the magnets is made small, the battery is preventedfrom being overcharged at high rotating speed, a fact which obviates theneed to use the voltage-reducing circuit.

[0024] As an embodiment of the present invention, a ferromagneticmaterial is further applied to that surface side of the rotor yoke whichdoes not face the coils.

[0025] According to the embodiment structured as described, the rotoryoke is improved in mechanical strength and also the flux leakage fromthe magnet can be prevented.

[0026] According to the present invention, there is provided a rotaryelectric machine comprising a stator having a plurality of coilsarranged in a substantially circular form around an axis and a rotorrotatable about the axis relative to the stator, wherein the rotorcomprises a rotor yoke facing the coils and having a gap in axialdirection, and wherein the rotor yoke is made of a circular disc of aferromagnetic material, wherein N-pole magnets and S-pole magnets aremounted alternately in the circumferential direction on a surface of therotor yoke facing the coils, and wherein salient portions facing theteeth of the coils are provided at predetermined intervals inpredetermined positions in the circumferential direction of an outerperiphery of the rotor yoke.

[0027] In this invention, as described, salient portions are providedalong the outer periphery of the rotor yoke. As a result, a reluctancetorque can be generated in collaboration with the teeth of the statorside, so that it is possible to widen the range of rotation speed of themotor.

[0028] Further according to this invention, the magnetic force of themagnet can be made weaker than before, but a reluctance torque can begenerated as described above. Therefore, when this invention is appliedin forming a starter-motor-cum-generator for vehicles, such asmotorcycles, a high torque is obtained by using a reluctance torque atlow rotating speed (when starting a car), and when this electric machineis rotated at high speed, because the magnetic force of the magnet ismade small, the battery is prevented from being overcharged and avoltage-reducing circuit is not required.

[0029] As an embodiment of the present invention, the above-mentionedsalient portions are formed as bent portions bent toward the statorside.

[0030] According to this embodiment, the bent portions are providedalong the outer periphery of the rotor yoke. Therefore, if a motor isformed according to this embodiment, a reluctance torque can begenerated at the bent portions on the rotor yoke side in collaborationwith the teeth on the stator side, and therefore it is possible toincrease the range of rotation speed.

[0031] Further according to the present invention, there is provided arotary electric machine comprising a stator having a plurality of coilsarranged in a substantially circular form around an axis and a rotorrotatable about the axis relative to the stator, wherein the rotorcomprises a rotor yoke facing the coils and having a gap in axialdirection, wherein the rotor yoke is made of a circular disc of aferromagnetic material, and wherein a hollow part, in which a rotatingshaft is press-fitted, is formed in the center of the rotor yoke in amanner integrally with the rotor yoke and a circularly curved surface isformed at an extreme end of the hollow part.

[0032] According to the present invention structured as described, thecircularly curved surface at the extreme end of hollow part may be usedas a bearing to bear a thrust, and the rotor and the thrust bearing maybe combined into a single structure, by which the rigidity of thestructure for rotating the rotor can be improved.

BRIEF DESCRIPTION OF THE DRAWINGS

[0033]FIG. 1 is a sectional view showing the whole structure of anaxial-gap motor according to a first embodiment of a rotary electricmachine of the present invention;

[0034]FIG. 2 is a plan view of the rotor in FIG. 1 as viewed from thestator side;

[0035]FIG. 3 is a fragmentary sectional view, taken in circumferentialdirection, of an essential part of the rotor in FIG. 2;

[0036]FIG. 4 is a plan view showing the structure of the rotor of anaxial-gap motor as viewed from the stator side according to a secondembodiment of a rotary electric machine of the present invention;

[0037]FIG. 5 is a fragmentary sectional view, taken in circumferentialdirection, of an essential part of the rotor in FIG. 4;

[0038]FIG. 6 is a sectional view of an essential part showing amodification of the rotor shown in FIG. 4;

[0039]FIG. 7 is a sectional view showing the whole structure of anaxial-gap motor according to a third embodiment of a rotary electricmachine of the present invention;

[0040]FIG. 8 is a plan view of the rotor in FIG. 7 as viewed from thestator side;

[0041]FIG. 9 is a sectional view showing the whole structure of anaxial-gap motor according to a fourth embodiment of a rotary electricmachine of the present invention;

[0042]FIG. 10 is a plan view of the rotor in FIG. 9 as viewed from thestator side;

[0043]FIG. 11 is a sectional view showing the whole structure of anaxial-gap motor according to a fifth embodiment of a rotary electricmachine of the present invention;

[0044]FIG. 12 is a plan view of the rotor in FIG. 11 as viewed from thestator side;

[0045]FIG. 13 is a sectional view showing an example of a conventionalaxial-gap motor; and

[0046]FIG. 14 is a plan view of the conventional rotor as viewed fromthe stator side.

BEST MODE FOR CARRYING OUT THE INVENTION

[0047] Embodiments of the present invention will be described withreference to the accompanying drawings.

[0048] Referring to FIGS. 1 to 3, the structure of a first embodimentwill be described in which the rotary electric machine of the presentinvention is applied to an axial-gap motor. A motor according to thefirst embodiment, which is disposed in a housing 1 as shown in FIG. 1,comprises a rotating shaft 7 rotatably supported by bearings 2, 3 fixedto the housing 1, a rotor 23 mounted integrally to the rotating shaft 7,and a stator 5 arranged facing the rotor 23 and fixed to the housing 1.

[0049] The stator 5 has a plurality of coils arranged in a substantiallycircular (annular) form about the rotating shaft 7. In other words, thestator 5 has an annular stator yoke 10 fixed to the housing 1. Aplurality of holes 10A are provided at predetermined intervals incircumferential direction of the stator yoke 10, and teeth 11 arepress-fitted into the holes 10A. The stator teeth 11 are each wound withcoils of wire 12.

[0050] The rotor 23 comprises a rotor yoke 26 made of a disc offerromagnetic material, such as iron, and the rotating shaft 7 ismounted at the center of the rotor yoke 26 and is rotatably supported ateach end by the bearings 2 and 3. On that surface area of the rotor yoke26 which faces the stator 5 exclusive of the center area (in otherwords, only on that area of the surface squarely facing the stator 5),the depressed portions 27 and the raised portions 28 are attached bybeing alternately arranged in circumferential direction of the rotoryoke 26 as shown in FIG. 3. In the depressed portions 27, N-pole magnets29 and S-pole magnets 30 are alternately placed and fixed as shown inFIGS. 2 and 3.

[0051] As described above, in the first embodiment, the N-pole magnets29 and the S-pole magnets 30 are arranged alternately on the rotor yoke26, the raised portions 28 are formed between the magnets 29 and 30, andthe raised portions 28 face the teeth 11 of the stator side 5.Therefore, according to the first embodiment, in addition to the torquegenerated by the magnets 29 and 30, the reluctance torque is generatedbetween the raised portions 28 on the rotor yoke side 26 and the teeth11 (coils) on the stator side 5, which makes it possible to increase therange of rotation speed of the motor.

[0052] Further according to the first embodiment, in which the raisedportions 28 are provided on the rotor yoke 26, the used quantity ofmagnet can be made smaller than before, and the production cost can bedecreased.

[0053] Meanwhile, when applied to vehicles, such as motorcycles, thefirst embodiment may be applied in forming astarter-motor-cum-generator. More specifically, the rotary electricmachine can be used as a starter motor to start the engine, and afterthe engine has started, it can be used as a generator.

[0054] On the other hand, according to the first embodiment, themagnetic force of the magnets 29, 30 can be made smaller than before,but a reluctance torque can be generated.

[0055] Therefore, when the first embodiment is applied in forming astarter-motor-cum-generator for vehicles, such as motorcycles, a hightorque can be obtained by this electric machine by using a reluctancetorque when it is operated at low rotating speed (when starting a car),and when this electric machine rotates at high rotating speed, becausethe magnetic force of the magnets 29, 30 is decreased, the battery isprevented from being overcharged, and therefore a voltage-reducingcircuit is not required.

[0056] Referring to FIGS. 4 and 5, description will be made of thestructure of a second embodiment in which the rotary electric machine ofthe present invention is applied to an axial-gap motor.

[0057] A motor according to the second embodiment is structured suchthat the rotor 23 of the motor of the first embodiment is used insteadof the rotor 33 shown in FIGS. 4 and 5; however, the other parts are thesame as in the motor according to the first embodiment and theirstructural descriptions are omitted.

[0058] As shown in FIG. 4, the rotor 33 comprises a disc rotor yoke 36made of ferromagnetic material, such as iron, and a rotating shaft 7 ismounted at the center of the rotor yoke 36.

[0059] The rotor yoke 36 has a corrugated region formed incircumferential direction of the rotor yoke except for the center regionthereof, the corrugated region has raised and depressed cross-sectionsalternating with each other in the circumferential direction of therotor yoke (Refer to FIG. 5). Therefore, as shown in FIG. 5, in thecircumferential direction of the rotor yoke 36, the depressed portions37 and the raised portions 38 are formed alternately on an upper surfaceside of the rotor yoke 36 and depressed portions 39 and raised portions40 are formed alternately on a lower surface side of the rotor yokefacing the stator (not shown).

[0060] On both surfaces of the corrugated region, magnets 41, 42 arearranged and fixed in the depressed portions 37, 39 as shown in FIG. 5.Further, the magnets 42 set in the depressed portions 39 on the lowersurface side are magnetized such that N-pole magnets and S-pole magnetsare formed (magnetized) alternately. The magnets 41, 42 shouldpreferably be anisotropic-magnetized.

[0061] As described above, according to the second embodiment, on thatsurface of the rotor yoke 36 which faces the stator, raised portions 40are arranged between the N-pole magnets and the S-pole magnets, and theraised portions 40 can face the matching teeth of the stator.

[0062] Therefore, according to the second embodiment, in addition to thetorque generated by the magnets 42, a reluctance torque is generatedbetween the raised portions 40 on the rotor yoke 36 side and the teethon the stator side, so that it is possible to increase the range ofrotation speed of the motor.

[0063] Moreover, according to the second embodiment, the rotor yoke 36can be produced at low cost by press working.

[0064] Further according to the second embodiment, the magnetic force ofthe magnets 41, 42 can be decreased, but a reluctance torque can begenerated as has been described.

[0065] Accordingly, when the first embodiment is applied in forming astarter-motor-cum-generator for a motorcycle or a similar vehicle, ahigh torque can be generated by using a reluctance torque at slowrotating speed (when starting a car), and when this rotary electricmachine is operated at high rotation speed, because the magnetic forceof the magnets 41, 42 is decreased, the battery can be prevented frombeing overcharged, and therefore a voltage-reducing circuit is notrequired.

[0066] A modified example of the rotor 33 will next be described withreference to FIG. 6.

[0067] A rotor 45 in FIG. 6 is formed by integrally attaching a disccore 46 of a ferromagnetic material to the upper surface of the rotor 33shown in FIGS. 4 and 5. Consequently, the mechanical strength of therotor 33 can be increased and it is possible to prevent magnetic fluxleakage from the magnets 41, 42.

[0068] Note that the other parts of the rotor 45 are identical instructure with those of the rotor 33 and the same components aredesignated by the same reference numerals, and their structuraldescriptions are omitted.

[0069] Referring to FIGS. 7 and 8, description will be made of thestructure of a third embodiment in which the rotary electric machine ofthe present invention is applied to an axial-gap motor.

[0070] A motor according to the third embodiment, which is disposed inthe housing 1 as shown in FIG. 7, comprises a rotating shaft 7 rotatablysupported by bearings 2, 3 fixed to the housing 1, a rotor 53 mountedintegrally to the rotating shaft 7, and a stator 5 arranged facing therotor 53 and fixed to the housing 1.

[0071] The rotor 53 comprises a rotor yoke 56 made of a disc of aferromagnetic material, such as iron, and the rotating shaft 7 ismounted at the center of the rotor yoke 56 and rotatably supported atboth ends thereof by the bearings 2, 3. On that surface which faces thestator 5 of the rotor yoke 56 exclusive of the center area and theperipheral area (in other words, only on that area of the surface areasquarely facing the stator 5), N-pole magnets 59 and S-pole magnets 60are attached by being alternately arranged in the circumferentialdirection as shown in FIG. 8.

[0072] Radially-salient portions 58 are formed integrally with the rotoryoke 56 at the positions on the outer circumference of the rotor yoke 56where the outer circumference is intersected by extensions of theboundaries between the N-pole magnets 59 and the S-pole magnets 60, asshown in FIGS. 7 and 8. Those salient portions 58 are provided togenerate reluctance torque in collaboration with the teeth of the stator5.

[0073] The stator 5 is basically the same in structure as the stator 5shown in FIG. 1, but since the salient portions 58 are added to therotor yoke 56, the salient portions 11A to generate reluctance torque bycoming to face the salient portions 58 are added to the teeth 11 of thestator.

[0074] As described above, according to the third embodiment, thesalient portions 58 are added to the outer periphery of the rotor yoke56, and the salient portions 58 come round to face the salient portions11A of the teeth 11 of the stator side 5. Therefore, according to thethird embodiment, in addition to the torque generated by the magnets 59and 60, reluctance torque is generated between the salient portions 58of the rotor yoke 56 and the salient portions 11A of the teeth on thestator side 5, and therefore it is possible to increase the range ofrotation speed of the motor.

[0075] Because the salient portions 58 are added to the outercircumference of the rotor yoke 56 in the third embodiment, their phasepositions relative to those of the magnets 59, 60 can be optimized.

[0076] Further, according to the third embodiment, the magnetic force ofthe magnets 59, 60 can be decreased, but reluctance torque can begenerated as described above.

[0077] Therefore, when the first embodiment is applied in forming astarter-motor-cum-generator for vehicles, such as motorcycles, a hightorque can be obtained by using reluctance torque when thismotor/generator is rotated at low rotation speed (when starting a car),and when this motor/generator is rotated at high speed, because themagnetic force of the magnets 59, 60 is decreased, the battery can beprevented from being overcharged, and therefore a voltage-reducingcircuit is not required.

[0078] Referring to FIGS. 9 and 10, description will be made of a fourthembodiment in which the rotary electric machine of the present inventionis applied to an axial-gap motor.

[0079] The motor according to the fourth embodiment, which is disposedin the housing 1 s shown in FIG. 9, comprises a rotating shaft 7rotatably supported by bearings 2, 3 fixed to the housing 1, a rotor 63integrally attached to the rotating shaft 7, and a stator 5 arrangedfacing the rotor 63 and fixed to the housing 1.

[0080] The rotor 63 is made of a circular-disc rotor yoke 66 of aferromagnetic material, such as iron, and the rotating shaft 7 ismounted at the center of the rotor yoke 66 and rotatably supported atboth ends thereof by the bearings 2, 3. On that surface area of therotor yoke 66 which faces the stator 5 exclusive of the center area andthe peripheral area (in other words, only on that area of the surfacesquarely facing the stator 5), the N-pole magnets 69 and the S-polemagnets 70 are arranged alternately in the circumferential direction ofthe rotor yoke 66 as shown in FIG. 10.

[0081] As shown in FIGS. 9 and 10, bent portions 68 bent down at rightangle to the stator side 5 are provided integrally with the rotor yoke66 at positions on the outer circumference of the rotor yoke 66 wherethe outer circumference is intersected by extensions of the boundariesbetween the N-pole magnets 69 and the magnets 70. Those bent portions 68are provided to generate reluctance torque in collaboration with theteeth of the stator 5.

[0082] The stator 5 is basically the same in structure as that of thestator 5 shown in FIG. 1, but because the bent portions 68 are added tothe rotor yoke 66, the teeth 11 are so formed as to generate reluctancetorque as they face the bent portions 68.

[0083] As described above, according to the fourth embodiment, the bentportions 68 are formed on the rotor yoke 66, those bent portions 68 comeround to face the teeth 11 of the stator side 5. As a result, accordingto the fourth embodiment, besides the torque generated by the magnets 69and 70, reluctance torque is generated between the bent portions 68 onthe rotor yoke 66, so that it is possible to enlarge the range ofrotation speed of the motor.

[0084] Further according to the fourth embodiment, since the bentportions 68 are added to the outer circumference of the rotor yoke 66,their phase positions relative to those of the magnets 69 and 70 can beoptimized.

[0085] Further according to the fourth embodiment, because the bentportions 68 are formed on the rotor yoke 66 in a manner to generatereluctance torque, compared with third embodiment, the diameter of therotor 63 can be made smaller, and as a result, the diameter of the wholemotor can be made smaller.

[0086] Moreover, according to the fourth embodiment, the magnetic forceof the magnets 69 and 70 can be decreased, but the reluctance torque canbe generated as described above.

[0087] Consequently, when the first embodiment is applied in forming astarter-motor-cum-generator for use in vehicles, such as motorcycles, ahigh torque can be obtained by using reluctance torque when thismotor/generator is running at low speed (as in starting a car), and whenthe motor/generator is running at high speed, because the magnetic forceof the magnets 69 and 70 is deceased, the battery can be prevented frombeing overcharged, making it unnecessary to use a voltage-reducingcircuit.

[0088] Referring to FIGS. 11 and 12, description will be made of a fifthembodiment in which the rotary electric machine of the present inventionis applied to an axial-gap motor.

[0089] The motor according to the fifth embodiment, which is disposed inthe housing 1 as shown in FIG. 11, comprises a rotor 73 rotatablysupported by bearings 2 and 3 fixed to the housing 1, and a stator 5arranged facing the rotor 73 and fixed to the housing 1.

[0090] The rotor 73 includes a rotor yoke 76 and a rotating shaft 7 asshown in FIGS. 11 and 12. The rotor yoke 76 is formed of a disc entirelymade of a ferromagnetic material, and a hollow part 74, in which arotating shaft 7 is press-fitted, is formed in a manner integrally withthe rotor yoke 76. A semispherical part (circularly curved surface) 75is formed integrally with the hollow part 74 at an extreme end thereof,and the semispherical part 75 is used as a bearing to bear the thrust ofthe rotor 73.

[0091] The hollow part 74 and the semispherical part 75 are formed bydrawing when the rotor yoke 76 is formed in a monolithic body. Inaddition, the semispherical part 75 is hardened to increase itsmechanical strength.

[0092] The rotating shaft 7 is mounted integrally with the rotor yoke 76at the center thereof by being press-fitted into the hollow part 74. Therotating shaft 7 and the hollow part 74 are supported at one end by thebearing 2 or 3, and the semispherical part 75 is arranged as a bearingto bear the thrust of the rotor yoke 76.

[0093] On that surface of the rotor yoke 76 which faces the stator 5exclusive of the center area, N-pole magnets and S-pole magnets 80 areattached by being arranged alternately in circumferential direction ofthe rotor yoke 76 as shown in FIGS. 11 and 12.

[0094] The stator 5 is the same in structure as the stator shown in FIG.1, and the same components are designated by the same reference numeralsand their descriptions are omitted.

[0095] According to the fifth embodiment, the semispherical part 75formed integrally with an extreme end of the hollow part 74 can be usedas a bearing to bear the thrust, and further the thrust bearing can beformed integrally with the rotor yoke 76. By this arrangement, therigidity of the structure for rotation of the rotor 73 can be improved.

[0096] The rotor 73 of the fifth embodiment is designed based on theconventional rotor 4 shown in FIG. 13 and is structured by being addedwith the hollow part 74 and the semispherical part 75.

[0097] However, alternatively, it is possible to use the rotor based onthe rotor 23, 33, 45, 53 or 63 according to the first to fourthembodiments, and add the hollow part 74 and the semispherical part 75.

[0098] In the first to fifth embodiments, description has been made ofcases where the rotary electric machine of the present invention isapplied to an axial-gap motor and cases where astarter-motor-cum-generator for vehicles, such as motorcycles, is formedby this rotary electric machine. However, the rotary electric machineaccording to the present invention can be applied as power generators ofthe types mentioned above, in which case the structure of such agenerator will be substantially the same structure of the relevantembodiment.

INDUSTRIAL APPLICABILITY

[0099] According to the present invention, when the present invention isapplied as a motor, reluctance torque can be generated between theraised portions on the rotor yoke side and the teeth (coils) on thestator side, for example, by which it is possible to increase the rangeof rotation speed of the motor.

[0100] Further, according to the present invention, when the presentinvention is applied in forming a starter-motor-cum-generator forvehicles, such as motorcycles, a high torque can be obtained by usingreluctance torque when this motor/generator operates at low rotationspeed (as in starting a car), and when this motor/generator operates athigh rotation speed, because the magnetic force of the magnets is madesmaller, overcharging can be prevented and a voltage-reducing circuit isnot required.

1. A rotary electric machine comprising a stator having a plurality of coils arranged in a substantially circular form around an axis and a rotor rotatable about said axis relative to said stator, wherein said rotor comprises a rotor yoke facing said coils and having a gap in axial direction, wherein said rotor yoke is made of a circular disc of a ferromagnetic material, and wherein depressed and raised portions are provided alternately in a circumferential direction on a surface of said rotor yoke facing said coils, and N-pole magnets and S-pole magnets are alternately arranged in said depressed portions.
 2. A rotary electric machine comprising a stator having a plurality of coils arranged in a substantially circular form around an axis and a rotor rotatable about said axis relative to said stator, wherein said rotor comprises a rotor yoke facing said coils and having a gap in axial direction, wherein said rotor yoke is made of a circular disc of a ferromagnetic material, and wherein a corrugated region having depressed and raised portions alternating with each other is formed in a circumferential direction of said rotor yoke and magnets are arranged in said depressed portions, and wherein out of all depressed portions, in those depressed portions on a surface side of said rotor yoke facing said coils, N-pole magnets and S-pole magnets are arranged alternately.
 3. A rotary electric machine according to claim 2, wherein a ferromagnetic material is further applied to that surface side of said rotor yoke which does not face said coils.
 4. A rotary electric machine comprising a stator having a plurality of coils arranged in a substantially circular form around an axis and a rotor rotatable about said axis relative to said stator, wherein said rotor comprises a rotor yoke facing said coils and having a gap in axial direction, wherein said rotor yoke is made of a circular disc of a ferromagnetic material, wherein N-pole magnets and S-pole magnets are mounted alternately in the circumferential direction on a surface of said rotor yoke facing said coils, and wherein salient portions facing said teeth of said coils are provided at predetermined intervals in predetermined positions in the circumferential direction of an outer periphery of said rotor yoke.
 5. A rotary electric machine according to claim 4, wherein said salient portions are bent portions bent down to said stator side.
 6. A rotary electric machine comprising a stator having a plurality of coils arranged in a substantially circular form around an axis and a rotor rotatable about said axis relative to said stator, wherein said rotor comprises a rotor yoke facing said coils and having a gap in axial direction, wherein said rotor yoke is made of a circular disc of a ferromagnetic material, and wherein a hollow part, in which a rotating shaft is press-fitted, is formed in the center of said rotor yoke in a manner integrally with said rotor yoke and a circularly curved surface is formed at an extreme end of said hollow part. 